Conventionally, projections for the purpose of preventing incorrect insertion of electrical terminals have been formed on the terminals as a mechanism for detecting upside-down insertion, i.e., the so-called incorrect insertion, of the terminals. For example, electrical connectors of this type include the connector disclosed in Japanese Patent Publication No. 4-220970 as shown in FIG. 4. This electrical connector 100 has a housing 102 in which cavities 104 that accommodate terminals 150 are formed. Housing lances 106 which hold the terminals 150 in the cavities 104 by engaging with the terminals 150 are formed as part of the housing 102. The terminals 150 have projections 108 which are located on the opposite sides of the terminals 150 from the housing lances 106 when the terminals 150 are correctly inserted. These projections 108 are constructed so that when the terminals 150 are inserted upside down, i.e., when the terminals 150 are inserted into the cavities 104 with the projections 108 located on the lower sides of the terminals 150 with respect to the position shown in FIG. 4, the projections 108 contact the rear surface 110 of the housing 102 so that insertion is impossible. Alternatively, in cases where the cavities 104 have large dimensions capable of accommodating the projections 108, the projections 108 contact the stepped inclined surfaces 112 of double locking members 114 which form portions of the housing lances 106, so that further insertion of the terminals 150 is prevented.
In order to allow smooth insertion of the terminals, the portions of the housing lances 106 that project into the cavities are sometimes formed as gradually inclined surfaces, as for example in the electrical connector disclosed in Japanese UM Publication No. 63-37874. In such cases, there is a danger that the projections 108 used to prevent incorrect insertion may move forward along these gradually inclined surfaces without catching, thus passing the housing lances so that the terminals 150 are incorrectly inserted.